lecture 1 outline (ch. 5) i. membrane structure ii. permeability iii. transport across membranes a....
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Lecture 1 Outline (Ch. 5)
I. Membrane Structure
II. Permeability
III. Transport Across Membranes
A. Passive
B. Facilitated
C. Active
D. Bulk
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Membrane structure
1915, knew membrane made of lipids and proteins
• Reasoned that membrane = bilayer
Where to place proteins?
Lipid layer 1
Lipid layer 2
Proteins
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Membrane structure
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• freeze fracture
• proteins intact, one layer or other
• two layers look different
Membrane structure
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Experiment to determine membrane fluidity:
• marked membrane proteins mixed in hybrid cell
Membrane structure
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Membrane fluidity
• phospholipid f.a. “tails”: saturation affects fluidity
• cholesterol buffers temperature changes
Membrane structure
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“fluid mosaic model” – 1970s
• fluid – phospholipids move around
• mosaic – proteins embedded in membrane
Membrane structure
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• cell membrane – amphipathic - hydrophilic & hydrophobic
• membrane proteins inserted, also amphipathic
Membrane structure
hydrophilic
hydrophilic
hydrophobic
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Membrane Proteins
Membrane proteins:
- transmembrane – span membrane
Integral: inserted in membrane
Peripheral: next to membrane- inside or outside
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• Two transmembrane proteins: different structure
Bacteriorhodopsin: proton pump
Membrane structure
Bacterial pore protein
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Membrane Proteins
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Movement of molecules
Simple Diffusion: most basic force to move molecules
• Disperse until concentration equal in all areas
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• Small, non-polar molecules OK
ex. steroids, O2, CO2
Movement of molecules
Cell membranes only allow some molecules across w/out help:
• No charged, polar, or large molecules
ex. sugars, ions, water*
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Transport Across Membranes
Types of transport:
A. Passive transport
- Simple diffusion
- Facilitated diffusion
- Osmosis
B. Active transport
C. Bulk transport
• Energy Required?
• Directionality?
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• DOWN concentration gradient
• molecules equally distribute across available area by type
Passive Transport - Simple Diffusion
- non-polar molecules (steroids, O2, CO2)
• NO ENERGY required
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• DOWN concentration gradient
• molecules equally distribute but cross membrane with the help of a channel (a) or carrier (b) protein.
Passive Transport – Facilitated Diffusion
• NO ENERGY required
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• osmosis – movement of water across cell membrane
• water crosses cell membranes via special channels called aquaporins
Passive Transport - Osmosis
• moves into/out of cell until solute concentration is balanced
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Passive Transport - Osmosis
equal solutes in solution as in cell
more solutes in solution, than in cell
fewer solutes in solution, than in cell
In each situation below, does water have net movement, and which direction:
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• tonicity – # solutes in solution in relation to cell
- isotonic – equal solutes in solution
- hypertonic – more solutes in solution
animal cell
plant cell
- hypotonic – fewer solutes in solution
Passive Transport - Osmosis
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Paramecium example
• regulate water balance
• water into contractile vacuole
– water expelled
• pond water hypotonic
Passive Transport - Osmosis
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Scenario: in movie theater, watching a long movie.
You are: drinking water
You are: eating popcorn
What happens to your blood?
What happens to your blood?
Passive Transport - Osmosis
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• transport proteins
a. ion pumps (uniporters)
• Ex. Na-K ion pump
- Na+ ions: inside to out
b. symporter/antiporter
- K+ ions: outside to in
Active Transport
• UP/AGAINST concentration gradient
• ENERGY IS required
• antiporter: two molecules move opposite directions (UP gradient)
c. coupled transport
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• ATP used pump H+ ions out
*gradients – used by cell for energy potential
• against concentration and charge gradients
Active Transport - uniporter
• Ex. proton (H+) pump
• uniporter: ONE molecule UP gradient
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Active Transport – coupled transport
• Ex. Active glucose transporter
• Na+ diffusion used for glucose active transport
• Na+ moving DOWN concentration gradient
• Glucose moving UP concentration gradient
• coupled transport: one molecule UP gradient & other DOWN gradient (opposite directions)
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• phagocytosis – “food” in
• pinocytosis – water in
• Molecules moved IN - endocytosis
Bulk Transport• ENERGY IS required
• Several or large molecules
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Bulk Transport
• receptor-mediated endocytosis
– proteins bind molecules, vesicles inside
• Molecules moved OUT - exocytosis
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Self-Check
Type of transport
Energy required?
Movement direction?
Examples:
Simple diffusion no Down conc. gradient O2, CO2, non-polar molecules
Osmosis
Facilitated diffusion
Active transport
Bulk transport
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Lecture 1 Outline (Ch. 6)
I. Energy and Metabolism
II. Thermodynamics
A. 1st Law – conservation of energy
B. 2nd Law - entropy
III. Free Energy
IV. Chemical Reactions
V. Cellular Energy - ATP
VI. Enzymes
A. Function
B. Regulation
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What is Energy?
The capacity to cause change
Energy
Where does energy on earth come from originally?
40 million billion calories per second!
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Metabolism
Metabolism –chemical conversions in an organism
Types of Energy:
- Kinetic Energy = energy of movement - thermal
- Potential = stored energy - chemical
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Potential energy can be converted to kinetic energy (& vice versa)
Potential Energy Kinetic Energy
Thermodynamics
Thermodynamics – study of energy transformation in a system
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Laws of ThermodynamicsLaws of Thermodynamics:: Explain the characteristics of energy
1st Law:
• Energy is conserved
• Energy is not created or destroyed
• Energy can be converted (Chemical Heat)
2nd Law: • During conversions, amount of useful energy decreases
• No process is 100% efficient
Thermodynamics
Energy is converted from more useful to less useful forms
• Entropy (measure of disorder) is increased
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Metabolic reactions: Chemical reactions in organism
Anabolic = builds
up molecules
Metabolism
Two Types of Metabolic Reactions:
Catabolic = breaks
down molecules
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Chemical Reactions:
• Like home offices – tend toward disorder
Chemical Reactions
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Chemical Reactions:
• Endergonic – energy required to complete reaction
• Exergonic – energy given off
Exergonic
Endergonic
Chemical Reactions
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Chemical Reaction:
• Process that makes and breaks chemical bonds
+Reactants
+Products
Two Types of Chemical Reactions:
1) Exergonic = releases energy
2) Endergonic = requires energy
Chemical Reactions
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2. Endergonic reactions: “Energy in”
•Products have more energy than reactants
•Requires influx of energy
1. Exergonic reactions: “Energy out” • Reactants have more energy than products• Reaction releases energy
Chemical Reactions
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Chemical Reactions
• Exergonic reaction • Endergonic reaction
release free energy
spontaneous
intake free energy
non-spontaneous
Glucose CO2 + H20 CO2 + H20 Glucose
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Activation Energy: Energy required to “jumpstart” a chemical reaction
• Must overcome repulsion of molecules due to negative charged electrons
Nucleus Repel Nucleus
Nucleus Repel Nucleus
ActivationEnergy
ActivationEnergy
Chemical Reactions
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Exergonic Reaction: – Reactants have more energy than products
But will sugar spontaneously burst into flames? Activation energy:
Make sugar and O2 molecules collide
Chemical Reactions“Downhill” reactions
sugar + O2
water + CO2
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Cellular Energy - ATP
• ATP = adenosine triphosphate
• ribose, adenine, 3 phosphates
• last (terminal) phosphate - removable
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• ATP hydrolyzed to ADP
ATP + H2O ADP + Pi
• Energy released, coupled to another chemical reaction
Cellular Energy - ATP
• stores 7.3 calories per mole
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• ATP regenerated
• need 7.3 kcal/mol to build ATP
• cells power building ATP by coupling to exergonic reactions
- cellular respiration
Cellular Energy - ATP
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Enzymes
Energy of activation (EA)
• reactants – absorb energy called: EA
• Reach EA, reaction proceeds (limiting step)
Exergonic – energy given off
• EA from ambient heat usually insufficient
• This is GOOD!
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Enzymes
Enzymes
• lower EA
• only for specific rxns
• cell chooses which reactions go forward!
enzymes:
-do speed up rxn would occur anyway
-do not make endergonic exergonic
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Enzymes
• enzyme – specific to substrate
• active site – part of enzyme -substrate
• binding tightens fit – induced fit
• form enzyme-substrate complex
• catalytic part of enzyme: converts reactant(s) to product(s)
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Enzymes
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Enzymes
• substrate(s) enter
• Enzymes lowers EA by:
• products formed
-template orientation
-stress bonds
-microenvironment
• enzyme reused
• What factors might affect enzyme activity?
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Enzymes
• inhibitors:
• Drug – blocks HIV enzyme at the active site
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Feedback Inhibition:
Enzymes
Like your furnace:
Detector
warm room
Furnace turns on
Room is warm
cold room
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Lecture 1 Summary1. Membrane composition and function (Ch. 5)
- Phospholipids and cholesterol- Integral and peripheral proteins
2. How molecules cross membranes (Ch. 5)- Passive Transport- Active Transport- Bulk Transport
3. Energy (Ch. 6)- Types, conversion
4. Metabolic/chemical reactions (Ch. 6)- Catabolic/Endergonic- Anabolic/Exergonic
5. ATP (Ch. 6)
6. Enzymes (Ch. 6)- Purpose- Function- Regulation